Aluminum photographic surfaces



06h 1956 M. L. FREEDMAN ET Al.

ALUMINUM PHOTOGRAPHIC SURFACES Filed Jan. 19, 1952 Aluminum Oxide Cooling Aluminum Bose Afier Anodic Oxidolion.

Aqueous Solution Of Silver Soil Conloining Diffusion -Oonlrolling Material Aluminum Oxide Afler Impregnoilon with Silver Soil Silver Holicle Formed In Silu In The Pores Of The Oxide Cooling Aluminum Oxide Cooling Aluminum Bose Afler Treolmenl With Aqueous Solution Of Alkali Metal Halide INVENTORS. MEYER L. FREEDMAN BYMARTIN A. uzvmm mew ALUMiNin/r rrrorooRArnrc SURFACES Meyer L. Freedman and Martin A. Levitin, Cleveland, Ohio, assignors to Horizons Incorporated, Cieveiand, Ohio, a corporation of New Jersey Application January 19, B52, Serial No. 267,360

(Claims. (Cl. 95-8) The possibility of treating surfaces of aluminum and aluminum alloys so that these are made photo-sensitive for picture-making purposes has been known for some time. In the known procedure, an aluminum base is first prepared with an adherent porous oxidized surface, and then this porous surface is treated chemically to produce a light-sensitive medium in which the light-sensitive salts are bound by the porous surface. The images are then obtained as by conventional practice with other lightsensitized surfaces. Thus, in U. S. Patent No. 2,115,339 an aluminum plate is subjected to oxidation, such as by anodic oxidation in an electrolytic cell, using for instance a 7 percent sulphuric acid electrolyte and a current of 0.01 to 0.4 amp. per square inch for about 30 minutes, while maintaining the temperature at -30 C. Then, a silver halide salt, such a silver chloride, silver bromide or silver iodide or mixtures, is deposited as an adsorbed salt in the oxide coating by a double decomposition reaction, or as a photographic gelatin or wet plate emulsion on the surface of the oxide coating. Unfortunately, in such known practice, the prepared sensitized surface is not durable or storageable, but must be used on the old wet plate schedule. Sensitized aluminum surfaces oifer advantages for certain usages for photographic results if the fundamental handicap of proclivity to fog, and in general lack of storageability were obviated. Unless plates made according to the old practice were exposed and developed within a short time in minutes, fogging occurs completely even though the plate were kept in the dark without exposure to light or developing chemicals. Also, such plates are not amenable to the standard range of photographic developers for the reason that chemical fog occurs so rapidly as to obscure the image. Such plates accordingly have had very limited possibilities because of their lack of stability. By the present invention, it now becomes possible to prepare sensitized surfaces on aluminum, capable of storageability and exposing at convenient times and developing as with other surfaces. Other objects and advantages of the invention will appear from the following description.

To the accomplishment of the foregoing and related ends, said invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed. The several stages of the practice of the invention are illustrated in the drawing in which Fig. 1 shows the condition of the surface of the aluminum base material after anodic oxidation;

Fig. 2 shows the impregnation of the oxidized surface of the aluminum base with an aqueous solution of a silver salt containing a diffusion-controlling material; and

Fig. 3 shows the silver halide formed in situ in the oxidized surface of the aluminum base after subsequent treatment with an aqueous solution of an alkali metal halide.

* nited States Patent O We have found that in the heretofore known practice, the oxidizing procedure has not provided an oxide coating which is sufliciently tight and complete, as well as adsor bent, to prevent side-reaction between the light-sensitive agent and aluminum at the bottom of the pores in the oxide coating. Oxidation of aluminum has heretofore been directed to meeting an anti-corrosion requirement, and in this an average result in an oxidized coating is sufficiently satisfactory. However, for an oxidized coating to meet the requirements of a storageable light-sensitized aluminum surface, much more than this is necessary. In our process, a tightly adherent and highly adsorbent oxide coating is formed, without the minute exposed aluminum areas at the base of the pores as heretofore. And in the further course of providing the light sensitive silver agent we apply a diffusion-barrier which prevents any possible dilfusing away of water-soluble silver salt. Such coatings are not only hard, adherent and effectively sealing against the aluminum, but are highly adsorbent for light-sensitizing salts in solution.

For the initial oxidizing of the aluminum surface, we may apply anodic oxidation in an electrolytic cell, or treat with an oxidizing agent in solution, or treat with fused salts. Thus, for instance the aluminum may be anodized in an electrolyte of a mixture of oxalic acid and oxalates of alkali metals, at a pH of 1 to 5, current density 0.5 to 5 amp. per square decimeter, and temperature 40 to C. Direct current is preferred, but alternating current may be used. Coatings made in this way are hard, adherent, but are highly adsorbent for soaking up the liquids and salts in solution. Or, the aluminum surface may be oxidized by treating with a solution of an effective oxidizing agent, such as alkali metal dichromates, chromates, ferricyanides, etc. After the aluminum surface has been initially oxidized, it is in any case next by our process subjected to treatment which is of a further oxidizing nature penetrating to and modifying the aluminum surface to a depth of several molecules thickness so that it is then impossible for any microscopic areas of metallic aluminum to be exposed at the base of the pores. This treatment involves an energetic oxidizing agent, such as solutions of salts containing oxygen and a polyvalent metal in the acid radical, as ferricyanides, dichromates, or chromates of alkali metals, in concentrations of 0.01 to 10 percent. After washing and drying, the prepared oxidized aluminum surface is dipped into a solution containing a water-soluble salt of silver, and the final lightsensitive agent is formed within the body of the coating and not on the surface. On this basis, the image-produc ing agent is locked in place and cannot be rubbed off by abrasion of the surface. In double decomposition reaction for formation of the silver halide in the oxidized coating, we include a diffusion-barrier which controls the diffusion rate of the water soluble salts. If this is not provided, it is found that when the plate is first immersed in a solution of silver nitrate and then subsequently immersed in alkali halide, the silver nitrate initially introduced diffuses so rapidly that the greater part of the silver halide is formed in coarse crystals on the outermost surface of the porous oxide film. But by providing the diffusion-barrier, the diffusion of the soluble salt or silver nitrate is controlled so that the subse: quent alkali halide in solution reacts by double decomposition to form the insoluble halide in distribution through the oxide coating rather than at the surface. Maximum effectiveness of the silver halide is thus obtained, and the fact that the silver halide is below the surface enables the image to be protected by heat-sealing technique ultimately. As afore-stated, contactand reaction of the silver halide with metallic aluminum is pre vented so that it is impossible for the silver halide to react with metallic aluminum.- The diffusion-barrier a very dilute solution of a hydrocolloid, such as polyvinyl alcohol, methyl cellulose, gum arabic, purified gelatin, etc., in concentration less than 2 percent, and preferably in the range of 0.1 to 0.5 percent. It is particularly noticedhere that this is altogether in contrast to any applying of a coating of gelatin silver halide emulsion. We are not applying a coating, nor any halide of silver emulsion. And whereas gelatin in standard photographic emulsion practice is employed in high concentration, as a requisite for coating, in our practice here the colloid function and dilute solution is what is involved. Where desired, after the aluminum surface has been oxidized to a suitable coating as mentioned, it is then dipped in a solution containing a water soluble silver salt, a minute amount of a hydrocolloid and also a small amount of an oxidizing agent. The plate is allowed to soak for a few minutes in such solution and is then dried. It is then dipped in a solution of an alkali halide which contains a small amount of an oxidizing agent. The alkali halides may be chlorides, bromides or iodides. A preferred procedure is to apply silver nitrate in solution, then an alkali chloride, and after silver chloride has been formed in the oxide coating, immerse the plate in an alkali bromide solution, or alkali iodide, or combinations of bromides and iodides. The soluble silver salt content of the first treating solution is high, on the order of to percent silver nitrate. An oxidizing agent used in combination with the soluble silver salt solution is very small, on the order of 0.01 to 0.03 percent of alkali metal ferricyanides, dichromates or chromates. After the plate is treated with a silver-containing solution together with a hydrocolloid diffusion-barrier and the oxidizing agent, the plate is allowed to dry without washing. By a modifi cation, instead of adding the oxidizing agent as water soluble alkali ferricyanides or chromates, the silver nitrate solution may be saturated with the silver salts of these oxidizing agents such as silver ferricyanide or silver chromate. In a further modification, the aluminum surface after being electrolytically anodized is then treated with a dilute solution of a strong oxidizing agent, such as chromic acid 1 to 10 percent, at an elevated temperature, e. g., to C. Then after washing and drying, the plate is subjected to sensitizing solutions as just described.

For the conversion of the soluble silver salt, e. g., nitrate, to halide, the potassium halides, bromide, chloride or iodide, are normally preferred, but the other alkali halides can be used. The alkali halides are in relatively strong solution, e. g., 5 to 25 percent, and the solution may also contain a minor amount of the same oxidizing agent as used in the first bath, and again such oxidizing agent is the alkali ferricyanide or dichromate. After the silver halide is formed in the coating of the aluminum, the plate is thoroughly washed in running water, dried, and stored in a light-tight container until ready for its photographic use. Such plate may be stored for even periods of years.

It goes without saying that all operations involving the deposition of the light-sensitive silver halide are carried out in a darkroom. In a useful modification, the deposition of silver chloride is preferred. And this is treated with solutions of alkali bromides or iodides or combinations of both. In some instances, it is useful to add a trace of silver nitrate to these halide or ripening solutions. This secondary ripening treatment particularly in the presence of a trace of silver nitrate further insures elimination of any fogging tendency. Again, after a silver halide is deposited, the plate may be treated with a solution of a mixture of alkali metal ferricyanide, bromide and'dichromate. This is a dilute solution containing approximately 1 percent each of potassium ferricyanide and bromideand approximately 0.2 percent of the dichromate.

The photographic plate thus obtained is exposed, developed and fixed in accordancev with standard photographic practice. The image may he toned inthe usual solutions containing gold, selenium, and the like to develop special effects. A final operation which is usually advisable, is to seal the surface so that it is permanently resistant to abrasion and scratching. This consists in immersing the plate in a boiling solution of salts such as sodium sulphate, sodium acetate, and the like, for 10 to 20 minutes. Where desired, the surface may be water-proofed also, by silicones, soap, and the like. Photographic plates made in accordance with the present process have excellent half-tone quality and an unusual degree of resolution. The photographic density is ample for duplication purposes and presents an article of permanence from a picture standpoint that is unique, both as to age possibility, wear, and temperature-resistance.

In all of the following examples which illustrate the process, a porous coating was first formed on an aluminum or aluminum alloy surface by electrolytic oxidation, preferably D. C. in which the bath consisted of a mixture of alkali oxalates and oxalic acid at a pH between 1.0 and S. The anodization was carried out at temperatures between 40 and 70 C. at current density 0.5 to 5 amp. per square decimeter. Under these conditions, after anodization for /2 to 1 hour, the highly porous film having a thickness between 0.0005 and 0.0015 in. was formed. If A. C. was used, a film thickness of 0.0002 to 0.0005 in. was obtained. Both techniques are useful. After the anodization, the plate was thoroughly washed in running water, then in a dilute solution of sodium hydroxide, 1 to 2 percent, and finally in running water, and then was dried at a temperature C. or below.

Example 1.A sheet of aluminum anodized as above is dipped for a few seconds into a 5% solution of chromic acid at 60 C. After washing and drying, all subsequent operations with the plate are carried out in the darkroom. In the darkroom, 30 grams of silver nitrate are dissolved in ccs. of distilled water. In addition, 0.5 gram of USP gelatin of photographic grade and 0.02 gram of potassium dichromate are also added to the solution and stirred until solution is complete. The dry anodized plate is soaked in this solution, allowed to drain, and excess solution wiped from the surface with a cotton swab. The plate is air dried and is then soaked for 1 minute in a solution consisting of 5 grams of potassium bromide and 5 grams of potassium dichromate in 100 ccs. of water. Any surface coating of silver bromide which might form in this treatment on the surface is wiped away while the plate is immersed in running water. The thoroughly washed plate is then oven dried at 50 C. and stored in the dark until use. Photographic exposure and development are those commonly known in the art.

Example 2.-A plate is treated with the silver nitrategelatin-dichromate mixture exactly as described in Example 1. It is then soaked for 10 seconds in a saturated solution of sodium chloride containing 5% potassium dichromate. After thorough washing, the plate is placed in a bath containing 12 /2 grams of potassium ferricyanide, 10 grams of potassium bromide and 2 grams of sodium dichromate, all dissolved in a liter of solution. It is retained in this bath for one minute. After rinsing in running water, the wet plate is then immersed in a 1% solution of potassium bromide for one minute. It is then washed vigorously, dried, and stored in the dark until use.

Example 3 .Same as Example 2 except that the ripening solution consists of a mixture of 0.5% potassium bromide and 0.5% potassium iodide.

Example 4.A suitable range of reagents for the silver nitrate steps are 0.1 to 2.0 grams of gelatin, 0.01 to 0.05 gram of potassium dichromate and 30 to 50 grams of silver nitrate per 100 ccs. of solution. The amount of oxidizing agent in the alkali halide bath may vary from 1 to 5% and the concentration of the alkali halide may vary from 10% up to saturation which is usually of the order of 40 to 50% if the bromides or iodides are in volved.

Example 5.The same procedure as described in Example 2 is followed except that the 1% potassium bromide bath used for ripening contains a trace of silver nitrate.

Example 6.-The same procedure as in Example 1 is followed except that the potassium bromide, potassium dichromate bath contains a trace of silver nitrate.

Example 7.The same procedure as above is followed except that the silver nitrate bath consists of the listed amounts of gelatin and silver nitrate. The oxidizing agent is afforded through the use of silver chromate with which the silver nitrate is saturated. The concentration of silver chromate is of the order of 0.01%.

In similar manner, instead of a dilute solution of gelatin mentioned, others of the hydrocolloids may be employed.

By the present procedure, the pinpoints of exposed aluminum at the base of anodized coats, due it is generally supposed to minute initial gas bubbles, are closed over; and in addition migration of silver salt ions of light sensitizer through to the aluminum under the oxide coat is colloidally barred. Reaction between light-sensitizer and aluminum is thus prevented. And as in the art of photography with glass plates the advent of the dry-plate process brought a long step advance in escape from the limitation of the immediate-use wet plate, here also aluminum is now freed from its initial limitation, and a dry non-fogging long-storageable product is had.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We therefore particularly point out and distinctly claim as our invention:

1. The method of producing an aluminum base photographic plate capable of being stored in darkness without fogging of its photosensitive element and further capable of being developed by conventional photographic procedure, said method comprising impregnating the pores of an anodically oxidized surface of a metallic aluminum base element with an aqueous solution of a silver salt further containing a minor amount but between at least about 0.1% and about 2% by weight of an organic hydrocolloid, so as to uniformly distribute said aqueous solution throughout the pores of the oxide coating, bringing the thus-impregnated oxidized surface of the base element into contact with an aqueous solution of an alkali metal halide with the resulting formation of the corresponding silver halide in situ in said pores and distributed throughout said pores, thereafter washing the thus-treated oxidized surface to remove any residual solution from the oxide pores, and drying the washed surface of the aluminum base element, all of said steps being carried out in the absence of light which would reduce the silver compound to metallic silver.

2. The method of producing an aluminum base photographic plate capable of being stored in darkness without fogging of its photosensitive element and further capable of being developed by conventional photographic procedure, said method comprising impregnating the pores of an anodically oxidized surface of a metallic aluminum base element with an aqueous solution of a silver salt further containing a minor amount but between at least about 0.1% and about 2% by weight of gelatin so as to uniformly distribute said aqueous solution throughout the pores of the oxide coating, bringing the thus-impregnated oxidized surface of the base element into contact with an aqueous solution of an alkali metal halide with the resulting formation of the corresponding silver halide in situ in said pores and distributed throughout said pores, thereafter washing the thus-treated oxidized surface to remove any residual solution from the oxide pores, and drying the washed surface of the aluminum base element, all of said steps being carried out in the absence of light which would reduce the silver compound to metallic silver.

3. The method of producing an aluminum base photographic plate capable of being stored in darkness Without fogging of its photosensitive element and further capable of being developed by conventional photographic procedure, said method comprising impregnating the pores of an anodically oxidized surface of a metallic aluminum base element with an aqueous solution of a. silver salt further containing a minor amount but between at least about 0.1% and about 2% by Weight of gelatin, so as to uniformly distribute said aqueous solution throughout the pores of the oxide coating, bringing the thusimpregnated oxidized surface of the base element into contact with an aqueous solution of an alkali metal halide with the resulting formation of the correspond-- ing silver halide in situ in said pores and distributed throughout said pores, thereafter washing the thus-treated oxidized surface to remove any residual solution from the oxide pores, immersing the resulting silver halidecontaining porous surface in an alkali metal halide solution for a period of at least about one minute, and drying the resulting surface-treated aluminum base element, all of said steps being carried out in the absence of light which would reduce the silver compound to metallic silver.

4. An aluminum base photographic plate capable of being stored in darkness without fogging of its photosensitive element and capable further of being developed by conventional photographic procedure produced by the process of claim 2.

5. An aluminum base photographic plate capable of being stored in darkness without fogging of its photosensitive element and capable further of being developed by conventional photographic procedure, produced by the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 240,262 Lutz Apr. 19, 1881 560,003 Martin May 12, 1896 1,946,151 Edwards Feb. 6, 1934 2,115,339 Mason Apr. 26, 1938 2,126,017 Jenny et al. Aug. 9, 1938 FOREIGN PATENTS 15,727 Great Britain Nov. 16, 1887 385,609 Great Britain Dec. 19, 1932 407,830 Great Britain Mar. 29, 1934 432,984 Great Britain Aug. 7, 1935 559,394 Great Britain Feb. 17, 1944 OTHER REFERENCES Anodizing Aluminum for Photography, The British Journal of Photography, vol. XC, June 18, 1943, page 226. (Copy in Div. 67; -8.) 

1. THE METHOD OF PRODUCING AN ALUMINUM BASE PHOTOGRAPHIC PLATE CAPABLE OF BEING STORED IN DARKNESS WITHOUT FOGGING OF ITS PHOTOSENSITIVE ELEMENT AND FURTHER CAPABLE OF BEING DEVELOPED BY CONVENTIONAL PHOTOGRAPHIC PROCEDURE, SAID METHOD COMPRISING IMPREGNATING THE PORES OF AN ANODICALLY OXIDIZED SURFACE OF A METALLIC ALUMINUM BASE ELEMENT WITH AN AQUEOUS SOLUTION OF A SILVER SALT FURTHER CONTAINING A MINOR AMOUNT BUT BETWEEN AT LEAST ABOUT 0.1% AND ABOUT 2% BY WEIGHT OF AN ORGANIC HYDROCOLLOID, SO AS TO UNIFORMLY DISTRIBUTE SAID AQUEOUS SOLUTION THROUGHOUT THE PORES OF THE OXIDE COATING, BRINGING THE THUS-IMPREGNATED OXIDIZED SURFACE OF THE BASE ELEMENT INTO CONTACT WITH AN AQUEOUS SOLUTION OF AN ALKALI METAL HALIDE WITH THE RESULTING FORMATION OF THE CORRESPONDING SILVER HALIDE IN SITU IN SAID PORES AND DISTRIBUTED THROUGHOUT SAID PORES, THEREAFTER WASHING THE THUS-TREATED OXIDIZED SURFACE TO REMOVE ANY RESIDUAL SOLUTION FROM THE OXIDE PORES, AND DRYING THE WASHED SURFACE OF THE ALUMINUM BASE ELEMENT, ALL OF SAID STEPS BEING CARRIED OUT IN THE ABSENCE OF LIGHT WHICH WOULD REDUCE THE SILVER COMPOUND TO METALLIC SILVER. 